Impact of mobility and effective mass on the thermoelectric performance of Ni doped Cu2Se

Abstract

Cu2Se, a liquid-like thermoelectric material, has shown tremendous promise in recent years due to its strong electrical properties and intrinsic low thermal conductivity, which might be optimized for future applications by engineering the performance of Cu ions. In the present study, the thermoelectric features of hydrothermally grown Cu2Se are modified by tuning the presence of nickel in the crystalline matrix. The approach of modifying electronic band structures has been explored to optimize carrier transports by balancing the competitive relationship between carrier mobility and effective mass in order to discover improvements in thermoelectric materials beyond nanostructures. Its exceptional thermoelectric performance stems from ultrahigh carrier mobility over the whole working temperature range, which is achieved by effectively modifying the transport parameters through Ni doping. The inclusion of nickel in the Cu2Se lattice at either substitutional or interstitial sites has a substantial influence on its thermal and electrical transport properties. A band sharpening caused by the presence of Ni in the lattice of Cu2Se tailored the carrier's effective mass, resulting in increased carrier mobility without compromising the carrier concentration. A simultaneous enhancement in the carrier concentration and carrier mobility is achieved due to the presence of Ni in the interstitial sites. A maximum power factor of 614 µW/mK2 is observed for the sample doped at 1.5 wt% Ni at 573 K. The lattice distortion and point defects caused by Ni substitution generated additional phonon scattering centers, resulting in a substantial decrease in thermal conductivity. The sample doped with 2 wt% Ni shows a maximum ZT value of 0.535 at 573 K, which is around 3 times higher than that of pristine Cu2Se. These findings show that nickel is a novel efficient dopant that may significantly increase the thermoelectric performance of Cu2Se via defect and band engineering.